Method and flow body with devices for suppressing sound generation when flowing over a cavity in a surface

Abstract

Method for suppressing the generation of sound at a cavity (3) in a surface (2) over which a flow (4) flows in a main flow direction (5), wherein at least one vortex (11) is generated in the flow (4) upstream of the cavity (3) in order to delay the reattachment of a boundary layer (8) of the flow (4) detaching at a leading edge (6) of the cavity (3) at least as far as a region of the surface (2) lying downstream of a trailing edge of the cavity (3), and wherein the at least one vortex (11) is generated outside the boundary layer (8) of the flow (4) with a vortex axis (12) running along the main flow direction (5) in such a way that a local flow component (13) in the at least one vortex (11) above the cavity (3) points away from the surface (2) adjacent to the cavity (3), characterized in thatthat each vortex (11) is generated at a wing tip (16) of a half-wing (14) oriented outside the boundary layer (8) along the surface (2) and transversely to the main flow direction (5) or a wing leading edge (18) of a half-delta wing (21) oriented outside the boundary layer (8) along the surface (2) and transversely to the main flow direction (5).

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to a method for suppressing the generation of sound during flow over a cavity in a surface, as well as to a flow body with devices for implementing this method. Furthermore, the invention relates to an aircraft and a general vehicle with such a flow body. In particular, the invention relates to a method having the features of the preamble of independent patent claim 1 and to a flow body having the features of the preamble of independent patent claim 5. STATE OF THE ART

[0002] When flowing over cavities that are embedded in surfaces over which flow occurs, acoustic resonances create sound of high sound pressure levels, which not only represent considerable noise but can also have harmful effects on neighboring components.

[0003] To suppress or attenuate the noise generated at a cavity over which fluid flows, it is known to shift the reattachment line of a highly turbulent boundary layer separating at an upstream leading edge of the cavity to a location on the surface downstream of a trailing edge of the cavity. This prevents interaction of the boundary layer with the trailing edge of the cavity.

[0004] To suppress noise generation at a weapons bay of an aircraft, US 2 749 064 A proposes a flap that deflects the flow away from the surface of the aircraft and a diffuser for part of the flow over the weapons bay.

[0005] US 6 098 925 A discloses an adaptive ramp on the leading edge of a weapons bay of an aircraft, which is extended when the weapons bay is opened.

[0006] From US 8 016 246 B2 the arrangement of a plasma actuator upstream of a weapon bay of an aircraft is known in order to deflect the boundary layer which separates at the upstream leading edge of this cavity away from the trailing edge of the cavity.

[0007] US Pat. No. 5,340,054 A discloses the suppression of noise generation at a cavity in a surface over which fluid flows by placing disruptive bodies within the boundary layer upstream of the leading edge of the cavity. The disruptive bodies are intended to prevent the generation and growth of vortices that cause acoustic oscillations.

[0008] The aforementioned measures to suppress noise generation at a flow-over cavity are often only effective in a limited flow velocity range, and they lead to both increased resistance and an increased radar signature, which is particularly disadvantageous in the military sector.

[0009] US 11 247 770 B2 discloses a vortex generator system and a method for assisting boundary layer separation from a vehicle, as well as an aircraft with a vortex generator system, which disclose the features of the preambles of independent patent claims 1 and 5. The vortex generator system has at least two vortex generators projecting from an outer contour of a vehicle surface at a location upstream of a leading edge of a cavity in the vehicle surface. The vortex generators are spaced apart from one another and aligned such that the vortex generators are closer together at their rear ends than at their front ends. The vortex generators are angled relative to a flow and configured to form a pair of counter-rotating vortices when the flow flows over the vortex generators.The counter-rotating vortices interact to force the boundary layer away from the vehicle as it exits the cavity. The vortex generators can be shaped like semi-delta wings and can be retracted into the surface or their angle of attack relative to the flow can be adjusted. The vortex generators projecting from the surface also influence the boundary layer, creating turbulence. OBJECT OF THE INVENTION

[0010] The invention is based on the object of demonstrating a method and flow body for suppressing the generation of sound at a cavity in a surface over which a flow is carried, in which the boundary layer of the flow is not disturbed or is specifically influenced. SOLUTION

[0011] The object of the invention is achieved by a method having the features of independent patent claim 1 and by a flow body having the features of independent patent claim 5. The dependent patent claims relate to preferred embodiments of the method according to the invention and the flow body according to the invention, wherein claims 9 and 10 are directed to an aircraft and a vehicle, respectively, with the flow body according to the invention. DESCRIPTION OF THE INVENTION

[0012] In a method according to the invention for suppressing the generation of sound at a cavity in a surface over which a flow flows in a main flow direction, in which at least one vortex is generated in the flow upstream of the cavity in order to delay the re-attachment of a boundary layer of the flow detaching at a leading edge of the cavity at least as far as a region of the surface lying downstream of a trailing edge of the cavity, the at least one vortex is generated outside the boundary layer of the flow with a vortex axis running along the main flow direction in such a way that a local flow component in the at least one vortex above the cavity points away from the surface adjacent to the cavity.

[0013] In other words, at least one longitudinal vortex is generated in the flow outside the boundary layer, the vortex axis of which, extending across the surface, is oriented relative to the cavity in such a way that a local flow component of the flow in the vortex points away from the surface adjacent to the cavity due to the circulation of the vortex around its vortex axis in the region above the cavity. In other words, the vortex induces a velocity in the direction away from the surface adjacent to the cavity that lifts the boundary layer, which separates at the leading edge of the cavity, above the cavity away from the surface adjacent to the cavity. As a result, the reattachment of the detached boundary layer to the surface - if it occurs at all - is delayed until a region of the surface downstream of the cavity.

[0014] The aforementioned effect can be induced with a single longitudinal vortex. However, preferably, a vortex pair consisting of two counter-rotating, i.e., counter-rotating vortices is generated in the flow upstream of the cavity. The local flow components of both counter-rotating vortices point between the vortex axes and thus above the cavity, away from the surface adjacent to the cavity.

[0015] Specifically, in the method according to the invention, each vortex is generated at a wing tip of a half-wing oriented transversely to the main flow direction, or at a wing leading edge of a half-delta wing oriented transversely to the main flow direction. The fact that the respective half-wing or half-delta wing is arranged transversely to the main flow direction does not necessarily mean that it must be perpendicular. Rather, it is sufficient that it is oriented transversely to the main flow direction to such an extent that the typical vortex formation occurs at the wing tip of the half-wing or at the leading edge of the half-delta wing, which is always swept anyway.

[0016] In the method according to the invention, each vortex is generated at a wing tip of a half-wing oriented outside the boundary layer along the surface or at a wing leading edge of a half-delta wing correspondingly oriented outside the boundary layer along the surface. A wing holder for holding the respective half-wing or half-delta wing can extend from the surface through the boundary layer to the half-wing or half-delta wing in such a way that the boundary layer is as undisturbed as possible by the wing holder. However, the wing holder can also be used to specifically influence the boundary layer. The fact that the respective half-wing or half-delta wing extends along the surface in this embodiment does not necessarily mean that the half-wing or half-delta wing must run parallel or even essentially parallel to the surface.To achieve this feature, it is sufficient for the respective half-wing or half-delta wing to have a significant component of its extension parallel to the surface. However, an at least approximately parallel alignment of the half-wing or half-delta wing to the surface is by no means excluded.

[0017] Specifically, a vortex pair consisting of counter-rotating vortices can be generated in the method according to the invention at the two wing tips of a wing or at the two leading edges of a delta wing. However, it is also possible, and can be quite advantageous, to generate the vortex pair consisting of counter-rotating vortices at two opposing wing tips of two half-wings or at the leading edges of two half-delta wings, in order to avoid having to arrange the respective wing holders upstream of the cavity.

[0018] In a flow body having a surface, a cavity in the surface having a trailing edge, and devices for suppressing the generation of sound at the cavity in the surface over which a flow flows in a main flow direction, wherein the devices have at least one vortex generator arranged upstream of the cavity, which is designed to generate at least one vortex in the flow in order to delay the re-attachment of a boundary layer of the flow separating at a leading edge of the cavity at least up to a region of the surface lying downstream of the trailing edge of the cavity, the at least one vortex generator is designed to generate the at least one vortex outside the boundary view of the flow with a vortex axis running along the main flow direction in such a way thatthat a local flow component in the at least one vortex above the cavity points away from the surface adjacent to the cavity.,

[0019] The at least one vortex generator is preferably designed to form a vortex pair consisting of two counter-rotating, i.e. counter-rotating vortices in the flow upstream of the cavity, wherein the local flow components between the vortex axes of the counter-rotating vortices point above the cavity away from the surface adjacent to the cavity.

[0020] To generate each vortex, the at least one vortex generator comprises a wing tip of a half-wing oriented transversely to the main flow direction or a wing leading edge of a half-delta wing oriented transversely to the main flow direction. The respective half-wing or half-delta wing runs along the surface.

[0021] Specifically, the at least one vortex generator for generating the pair of counter-rotating vortices can comprise a wing with two wing tips running along the surface or a delta wing with two wing leading edges. Alternatively, the at least one vortex generator for generating the vortex pair can comprise two opposing wing tips of two half-wings or wing leading edges of two half-delta wings.

[0022] In an aircraft with a flow body according to the invention, the cavity can be, for example, a landing gear bay or a weapons bay of the aircraft. The at least one vortex generator can be transferred from a retracted or inactive position to an extended or activated position as soon as the landing gear bay or weapons bay is opened. Thus, the vortex(es) generated by the at least one vortex generator are only generated when necessary to suppress the generation of noise at the open, overflow cavity. A vortex generator can be deactivated, for example, by reducing its angle of attack to zero relative to the main flow direction; it can be activated accordingly by appropriately adjusting its angle of attack.

[0023] In a vehicle with the flow body according to the invention, the cavity can end at the surface with a window opening or cabin opening forming the trailing edge. In this case, too, the at least one vortex generator can be retracted or remain inactive until it is needed to suppress noise generation when the window or cabin opening is open.

[0024] Advantageous further developments of the invention emerge from the patent claims, the description and the drawings.

[0025] The advantages of features and combinations of several features mentioned in the description are merely exemplary and can be effective alternatively or cumulatively, without the advantages necessarily having to be achieved by embodiments according to the invention.

[0026] With regard to the disclosure content – ​​not the scope of protection – of the original application documents and the patent, the following applies: Further features can be found in the drawings – in particular the illustrated geometries and the relative dimensions of several components to one another, as well as their relative arrangement and operative connection. The combination of features of different embodiments of the invention or features of different patent claims is also possible, deviating from the chosen references of the patent claims, and is hereby encouraged. This also applies to features that are illustrated in separate drawings or mentioned in their description. These features can also be combined with features of different patent claims.Likewise, features listed in the patent claims may be omitted for further embodiments of the invention, but this does not apply to the independent patent claims of the granted patent.

[0027] The number of features mentioned in the patent claims and the description is to be understood as meaning that exactly this number or a greater number than the stated number is present, without the need for the explicit use of the adverb "at least." Thus, for example, if reference is made to one cavity, this is to be understood as meaning that exactly one cavity, two cavities, or more cavities are present. The features mentioned in the patent claims may be supplemented by further features or may be the only features present in the subject matter of the respective patent claim.

[0028] The reference signs contained in the patent claims do not represent a limitation of the scope of the subject-matter protected by the patent claims. They serve solely to make the patent claims easier to understand. BRIEF DESCRIPTION OF THE CHARACTERS

[0029] In the following, the invention is further explained and described with reference to preferred embodiments shown in the figures. Fig. 1 shows a cavity in a surface of a flow body over which a flow flows and devices for suppressing sound generation at the overflowed cavity in a section along the main flow direction. Fig. Figure 2 shows the cavity and the device in a view of the overflow cavity from above. Fig. 3 shows a Fig. 2 corresponding view of a flowing cavity from above with other devices for suppressing sound generation at the cavity. Fig. 4 is a section through the overflow cavity according to Fig. 3 transverse to the main flow direction, looking against the main flow direction at the sound suppression devices arranged upstream of the cavity. Fig. Figures 5 to 7 are top views of the overflow cavity, each showing different devices for suppressing noise generation. FIGURE DESCRIPTION

[0030] Fig. 1 shows a region of a flow body 1 in whose surface 2 a cavity 3 is formed. When a flow 4 with a main flow direction 5 flows over the cavity 3 in the surface 2, a generally turbulent boundary layer 8 of the flow 4 detaches from the surface 2 at an upstream leading edge 6 of the cavity 3. When the detached boundary layer 8 impinges on a trailing edge 7 of the cavity, this is associated with the generation of sound with a high sound pressure level. This is particularly true when the boundary layer 8 is turbulent. In order to delay the re-attachment of the turbulent boundary layer 8 of the flow 4 at least to a region of the surface 2 lying downstream of the trailing edge 7, devices 9 for suppressing the generation of sound have a vortex generator 10.The vortex generator 10 is designed to generate a vortex 11 outside the boundary layer 8 with a vortex axis 12 running along the main flow direction 5. This vortex 11 has a local flow component 13 above the cavity 3, which is directed away from the surface 2 adjacent to the cavity 3. Due to this local flow component 13, the vortex 11 interacts with the turbulent boundary layer 8 in the desired manner, so that the boundary layer 8 is lifted away from the surface 2 and only reattaches itself to the surface 2 behind the trailing edge 7 - if at all. The vortex generator 10 is specifically a half-wing 14, which is held above the boundary layer 8 by a wing holder 15.The vortex 11 detaches from the wing tip 16 of the half-wing 14, which is positioned opposite the main flow direction 5; and its region with the flow component 13, which points away from the surface 2, extends over the cavity 3, where it lifts the turbulent boundary layer 8 away from the surface 2 in front of the trailing edge 7 to such an extent that it only attaches itself again to the surface 2 behind the trailing edge 7. The relative arrangement of the half-wing 14 with the wing tip 16 and the vortex 11 emanating from it with the vortex axis 12 to the cavity 3 is shown in the top view according to . Fig. 2.

[0031] The Fig. 3 and Fig. 4 shows devices 9 for suppressing noise generation at the cavity 3, in which the vortex generator 10 has a delta wing 17 with two wing leading edges 18, which generates two counter-rotating vortices 11. The two counter-rotating vortices 11 rotate in opposite directions around essentially parallel vortex axes 12. Above the cavity 3, both vortices have the local flow component 13, which is directed away from the surface adjacent to the cavity 3. The vortex pair 19 thus formed lifts the turbulent boundary layer 8 particularly effectively above the cavity 3, so that it only reattaches to the surface 2 behind the trailing edge 7 of the cavity 3.

[0032] As already mentioned in the Fig. 3 and Fig. 4 also show the following Fig. 5 to 7 do not have the wing holder(s) present there, which hold the respective wing beyond the boundary layer 8 above the surface 2. In Fig. 5, the vortex generator 10 is a wing 20 with two wing tips 16 pointing away from each other, at each of which one of two counter-rotating vortices 11 of the vortex pair 19 is generated.

[0033] According to Fig. 6, the devices 9 have two vortex generators 10, each in the form of a half-wing 14 with one of two mutually facing wing tips 16, at which the two counter-rotating vortices 11 of the vortex pair 19 are generated.

[0034] According to Fig. 7 are instead of the half-wings 14 according to Fig. 6 two half delta wings 14 with mutually facing wing leading edges 18 are provided as vortex generators 10 of the devices 9.

[0035] The cavity 3 can, for example, be a landing gear bay or a weapons bay of an aircraft. However, the cavity 3 can also end with a window opening or cabin opening forming the trailing edge 7 on the surface 2. LIST OF REFERENCE SYMBOLS 1 flow body 2 Surface 3 Cavity 4 Current 5 Main flow direction 6 leading edge 7 trailing edge 8 Boundary layer 9 facilities 10 vortex generator 11 vertebrae 12 Vortex axis 13 Flow component 14 half wings 15 wing holders 16 wingtip 17 delta wings 18 Wing leading edge 19 pairs of vertebrae 20 wings 21 half delta wing

Claims

[1] Method for suppressing sound generation at a cavity (3) in a surface (2) over which a flow (4) is subjected in a main flow direction (5), wherein at least one vortex (11) is generated upstream of the cavity (3) in the flow (4) in order to delay the reattachment of a boundary layer (8) of the flow (4) that detaches at a leading edge (6) of the cavity (3) at least as far as a region of the surface (2) located downstream of a trailing edge of the cavity (3), and wherein the at least one vortex (11) is generated outside the boundary layer (8) of the flow (4) with a vortex axis (12) extending along the main flow direction (5) such that a local flow component (13) in the at least one vortex (11) over the cavity (3) points away from the surface (2) adjacent to the cavity (3), characterized by, that each vortex (11) is generated at a wingtip (16) of a half-wing (14) oriented outside the boundary layer (8) along the surface (2) and transverse to the main flow direction (5) or at a wing leading edge (18) of a half-delta wing (21) oriented outside the boundary layer (8) along the surface (2) and transverse to the main flow direction (5). [2] Method according to claim 1, characterized by , that upstream of the cavity (3) a vortex pair (19) is generated from two counter-rotating vortices (11) in the flow (4), wherein the local flow components (13) between the vortex axes (12) of the counter-rotating vortices (11) above the cavity (3) point away from the surface (2) adjacent to the cavity (3). [3] Method according to claim 2, characterized by , that the vortex pair (19) is generated at the two wingtips (16) of a wing (20) or at the two wing leading edges (18) of a delta wing (17). [4] Method according to claim 2, characterized by , that the vortex pair (19) is generated at two oppositely directed wingtips (16) of two half-wings (14) or wing leading edges (18) of two half-delta wings (21). [5] Flow body (1) with - a surface (2), - a cavity (3) with a trailing edge (7) in the surface (2) and - Devices (9) for suppressing sound generation at the cavity (3) in the surface (2) over which a flow (4) in a main flow direction (5) flows, wherein the devices (9) comprise at least one vortex generator (10) arranged upstream of the cavity (3), which is configured to generate at least one vortex (11) in the flow (4) in order to delay the reattachment of a boundary layer (8) of the flow (4) that detaches at a leading edge (6) of the cavity (3) at least until a region of the surface (2) located downstream of the trailing edge (7) of the cavity (3), wherein the at least one vortex generator (10) is configured to generate the at least one vortex (11) outside the boundary layer (8) of the flow (4) with a vortex axis (12) extending along the main flow direction (5),that a local flow component (13) in the at least one vortex (11) above the cavity (3) points away from the surface (2) adjacent to the cavity (3), , characterized by , that the at least one vortex generator (10) for generating each vortex (11) has a wingtip (16) of a half-wing (14) oriented outside the boundary layer (8) along the surface (2) and transverse to the main flow direction (5) or a wing leading edge (18) of a half-delta wing (21) oriented outside the boundary layer (8) along the surface (2) and transverse to the main flow direction (5). [6] Flow body (1) according to claim 5, characterized by, that the at least one vortex generator (10) is configured to generate a vortex pair (19) of two counter-rotating vortices (11) in the flow (4) upstream of the cavity (3), wherein the local flow components (13) between the vortex axes (12) of the counter-rotating vortices (11) above the cavity (3) point away from the surface (2) adjacent to the cavity (3). [7] Flow body (1) according to claim 6, characterized by , that the at least one vortex generator (10) for generating the vortex pair (19) has a wing (20) extending along the surface (2) with two wingtips (16) or delta wing (17) with two wing leading edges (18). [8] Flow body (1) according to claim 6, characterized by , that the at least one vortex generator (10) for generating the vortex pair (19) has two oppositely directed wingtips (16) of two half-wings (14) or wing leading edges (18) of two half-delta wings (21). [9] Aircraft with a flow body (1) according to any one of claims 5 to 8, characterized by , that the cavity (3) is a landing gear bay or weapons bay of the aircraft. [10] Vehicle with a flow body (1) according to any one of claims 5 to 8, characterized by , that the cavity (3) ends at the surface (2) with a window opening or cabin opening forming the rear edge (7).

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